<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 500px;
            height: 400px;
           background-color: red;
           display: flex;
           justify-content: center;
           align-items: center;

        }
        span{
            width: 50px;
            height: 40px;
            background-color: green;

        }
    </style>
</head>
<body>
    <div>
        <span>哈哈</span>
        <span>嘻嘻</span>
        <span>呵呵</span>
    </div>
</body>
</html>